A U.S. Border Patrol agent in Arizona claims he was privy to classified intelligence that proves terrorists have infiltrated the homeland from Mexico.

Border agent Art Del Cueto, who heads the national union for border patrol agents Local 2544 in Tucson, made those comments in an interview with Public Radio International (PRI) that aired September 24.

While walking a section of the Arizona-Mexico border, Del Cueto told PRI that the area is susceptible to Islamic terrorist crossings, adding that classified U.S. Border Patrol intelligence verifies that some have successfully infiltrated the U.S .

Del Cueto did not elaborate further, saying the evidence is classified.

Border agents have to remain vigilant of terrorists coming across the southern border, according to Del Cueto.

“You have to,” he told PRI. “With the intel we’ve received and the training we’ve received, you have to be expecting it. You have to have that extra level of alertness.”

Conservative lawmakers such as Sen. Ted Cruz (R-Texas) have warned about potential Islamic State (IS, also known as ISIS and ISIL) activity along the U.S.-Mexico border.

“First and foremost, Washington should resolve to make border security a top priority finally, rather than an afterthought, of this plan in light of concerns about potential ISIS activities on our southern border, cited in a Texas Department of Public Safety bulletin reported by Fox News,” said Sen. Cruz in an opinion piece for CNN. “As long as our border isn’t secure, the government is making it far too easy for terrorists to infiltrate our nation.”

Breitbart Texas recently obtained a leaked document from the Texas Department of Public Safety warning federal border agents about an ISIS-related threat along the southwest border.

However, the Democrat lawmaker added, “It doesn’t mean there couldn’t at some time in the future be such a threat, it doesn’t mean we shouldn’t be vigilant, it just means at this point in time there is no threat, nor has there ever been.”